It is known that some n-butyric acid compounds have advantageous biological effects on the digestive system, stimulating the growth of the intestinal villi and modifying the development of gastro-enteric micro-organisms.
Butyric acid is a short-chain, monocarboxylic fatty acid (4 carbon-atom chain) which is also classified amongst the volatile fatty acids (VFAs) together with acetic acid (2 carbon-atom chain) and propionic acid (3 carbon-atom chain). Butyric acid has 2 isomers, n-butyric acid and isobutyric acid. At ambient temperature, n-butyric acid is in liquid form and also has a characteristic rancid butter odour which is noticed by humans and by many animal species even in very low concentrations.
Amongst the n-butyric acid compounds which are of greatest interest are its salts and its esters, which are generally referred to as “butyrates”, and in particular, its sodium salt.
N-butyric acid ester is commercially available in liquid form whereas the n-butyric acid sodium salt is commercially available both in liquid form (in 50% aqueous solution—as a direct product of the reaction for the synthesis of the sodium salt from n-butyric acid) and in solid granular form (as a white powder which is stable up to 250° C.).
Depending on the surrounding environment, n-butyric acid compounds may be in dissociated form or in non-dissociated form; the latter is of particular importance at the biological level since it can be absorbed by the intestinal walls and by the cell membranes of micro-organisms and can have a more marked effect than the dissociated form.
Butyrates are produced mainly from hydrocarbons (cellulose and starch) by fermentation in anaerobic conditions by various micro-organisms and this process also takes place in the large intestine. After its formation, the butyrate is partially metabolized and the non-metabolized fraction of the non-dissociated butyrate is absorbed in the large intestine and enters the circulation.
It can be seen from data reported in the literature that volatile fatty-acid salts can inhibit the growth of haemolytic Escherichia coli strains by up to 50% (Galfi P., Neogrady S., 1992).
Amongst these salts, n-butyric acid salts have the greatest inhibiting power and this increases with reduction in pH, which favours the presence of its non-dissociated form. It has come to light from studies on the effects of an n-butyric acid salt on various strains of micro-organisms of the digestive system (Galfi P., Neogrady S., 1991) that the reduction in the development of E. coli is due to a direct effect of the butyrate and to an increase in the development of Lactobacilli. The antimicrobial effect of this salt is therefore selective. Other micro-organisms that are sensitive to n-butyric acid salts and to pH are: Clostridium acetobutylicum, Escherichia coli, Streptococcus cremoris, Lactococcus lactis and cremoris, and Salmonella species, whereas Lactobacillus species and Streptococcus bovis are less sensitive.
Butyrate has a further biological effect, more precisely, a stimulating effect on the growth of the wall of the digestive system (Galfi P., Neogrady S., 1991).
These studies are supported by the results obtained from animal feed tests which show a greater daily increase in weight, an improved utilization of feeds, and reduced mortality.
Alongside their considerable capacities, however, n-butyric acid compounds have a considerable disadvantage due to the decidedly unpleasant rancid butter odour which characterizes the starting n-butyric acid and which complicates the production and storage processes.
In fact, these compounds do not have unpleasant odours per se but they are particularly sensitive to acid environments in which they can easily hydrolyze and reform the original n-butyric acid, with the above-mentioned disadvantages.
For this reason, if butyrate were administered as such to an animal or to a human being, n-butyric acid would immediately form at gastric level, rendering the butyrate no longer available for absorption at intestinal level.
To limit this problem, it is known to microencapsulate the butyrate by coating it with a lipid matrix.
EP1354520, in the name of the Applicant, discloses a granulated product having a core of butyrate microencapsulated in a lipid structure with buffer compounds such as carbonates and bicarbonates.
It is thus sought to protect the butyrate from any acid compounds present in the feed and, in particular, from the strongly acid environment that is present at gastric level, but to allow it to be released at intestinal level, by virtue of the degradative action of specific enzymes on the lipid matrix.
In spite of the excellence of the principle underlying this measure, the problem can be considered only partially solved, however, since a considerable fraction of the microencapsulated product is found to be degraded at gastric level. Moreover, the Applicant has also found that, particularly in the case of pig feed, some of the butyrate is also hydrolyzed during storage because of the presence of acid compounds in the feed.
WO 2008/098807, in the name of the Applicant, discloses a granulated product having a core of conjugated linoleic acid microencapsulated in a lipid matrix having a mineral agent structure comprising silica and optionally calcium carbonate or calcium sulphate dihydrate.
There is therefore still a need, in the technical field in question, to improve the process for the production of an n-butyric acid compound in microencapsulated form in order to improve the final characteristics of the product, in particular its resistance to acid environments.